A number of industrial processes produce vent gases or off-gases containing elemental sulfur. One example of such a process is the pressure oxidation of metal-bearing sulfide minerals. Pressure oxidation involves contacting a mineral slurry with an oxidant, such as oxygen gas, at elevated temperature and pressure in an autoclave to oxidize one or more of the minerals, thereby freeing metal values of interest for possible recovery in subsequent metal recovery operations. Where the mineral undergoing pressure oxidation is a sulfide ore, the sulfide sulfur of the ore is oxidized to one or more sulfur species, such as sulfate and/or elemental sulfur, depending on the process conditions and the specific ore being oxidized.
At the elevated temperatures and pressures of the oxidation reaction, elemental sulfur can exist in liquid or vapor form and is discharged from the autoclave as a component of the autoclave vent gas. After leaving the autoclave, the vent gas is typically passed through a gas scrubber and discharged to atmosphere. In more recently designed pressure oxidation plants, the vent gas is passed through an aqueous medium, typically water, inside a quench vessel to recover heat from the vent gas and to remove condensable materials, thereby reducing the volume of vent gas which must be treated by the gas scrubber. The elemental sulfur in the vent gas solidifies during quenching and is removed from the quench vessel with the aqueous medium containing the condensed fraction of the vent gas. The aqueous medium is drained from the quench vessel and may be subjected to further process steps such as neutralization, solids removal and/or heat recovery.
Elemental sulfur is known to exist in several different solid forms, known as allotropes. The predominant sulfur allotrope produced during rapid quenching of sulfur liquid or vapor is monoclinic sulfur, which tends to form a soft, sticky, amorphous mass and causes difficulties during subsequent processing of the aqueous medium drained from the quench vessel. In particular, monoclinic sulfur blinds filters used for recovery of solids and contributes to the scaling of process equipment such as heat exchangers which may be used to recover heat from the condensed vent gas.
Thus, there is a need for a sulfur removal process which avoids the formation of sticky allotropes of sulfur.